This invention relates to a plasma display apparatus and more particularly to means for driving AC refresh-type plasma display panel.
A typical example of a conventional AC refresh-type plasma display panel (PDP) which is to be used in the present invention comprises two glass plates having electrode groups which are coated with a dielectric layer. The two glass plates are arranged in a manner which makes electrode groups thereof opposed to each other. Electrodes in each group intersect each other perpendicularly to form a matrix display type. The glass plates are sealed air-tight with glass frits. Neon gas fills in the sealed space surronded by the glass plates.
When the driving circuit applies a pulsed voltage to only one electrode group while maintaining the other electrode group at potential zero discharge occurs between the electrodes. The voltage discharged at the cell which is the most easy to discharge within the PDP is defined as the minimum unilateral discharge voltage (VDmin). The voltage discharged at the cell which is the most unlikely to discharge within the PDP is defined as the maximum unilateral discharge voltage (VDmax). If one electrode group of the PDP has a first pulse train applied thereto with a high voltage (V.sub.0) which is higher than VDmin but lower than VDmax while the other electrode group has a second pulse train applied thereto with a low voltage (V1) which has a phase which is the same as or opposite to the first pulse train, the discharge does not occur when the relation holds; VDmin&gt;.vertline.V0.vertline.-.vertline.V1.vertline. and discharge occurs when the relation holds; VDmax&lt;.vertline.V0.vertline.+.vertline.V1.vertline..
U.S. Pat. No. 3,869,644 issued on Mar. 4, 1975 discloses a phase-select method using the above condition as one example of the prior art AC refresh-type driving circuits for plasma display panels (PDP). In this prior art driving circuit, while a first pulse train of high voltage is applied to scanning electrodes in a time division mode. A second pulse train of low voltage, having the phase opposite to the phase of the first pulse train, is applied to selected data electrodes associated with the cell which is selected to discharge. In addition, a third pulse train of low voltage having the phase which is the same as the phase of the first pulse train is applied to remaining data electrodes associated with non-selected cells so as not to discharge the non-selected cells, thereby securing a stable operation.
In this prior art driving circuit, however, driving circuits are electrically connected via stray capacities between adjacent data electrodes provided on the substrate of PDP. When the adjacent data electrodes are driven for discharging and non-discharging concurrently, the power consumption of the driving circuits for the adjacent data electrodes becomes maximum. Although the brightness of an AC refresh-type PDP is determined by the number of pulses contained in a unit time, the larger the number of pulses becomes, the larger the power consumption of the driving circuits becomes. Thus the restrictions on the driving frequency present a formidable obstacle in obtaining sufficient brightness.
The prior art driving circuit is further detrimental in that if there is mismatch in time of high frequency pulses between voltages applied to the scanning electrodes and the data electrodes, the range of the driving voltage becomes narrow.
Moreover, if transparent electrodes are used for data electrodes, a distributed constant circuit is formed via stray capacity between the transparent electrodes. As the waveforms and voltages at a top end of the transparent electrodes differ from the waveforms and voltage at an input end, the brightness fluctuates unevenly. This also causes a delay in time and changes in voltage between the first pulse train for the scanning side and the second and third pulse trains for the data side. The range of driving voltage inconveniently becomes narrower.